Abstract: The study was carried out to investigate pathotypes relationship of six Rice Yellow Mottle Virus (RYMV) isolates from North Central Zone of Nigeria in 2016 using some released Oryza species and Near Isogenic Lines (NILs). The experiment was laid out in a split-split plot design in the screen house at Badeggi, Niger State, Nigeria. Yield and agronomic data were subjected to statistical analysis using CropStat Version 7.2. The result showed a non-significant interaction effect of rice genotypes, disease isolates and inoculation regimes on spikelets sterility (%) and a highly significant effect (p = 0.01) on yield per plant (g) at harvest. The impact of the virus on the number of panicles per plant at maturity was significantly higher on test plants inoculated at active tillering stages which consistently produced lower mean panicle numbers across the levels of virus isolates. The result also showed that NIL 54 produced high resistance to the virus which is not due to immunity as the leaf extract from inoculated plant was infectious on susceptible FKR 28 during back inoculation test. NIL 54 did not also record significant reduction on the average leaf length (cm) per plant at maturity with the virus isolates; neither did it express the characteristic symptoms of the virus with the six isolates. Obubu-Ofu and Makurdi isolates circumvented the resistance in Gigante and showed obvious yellow mottle symptoms. The serological analysis and RYMV isolates characterization indicated that the six virus isolates belonged to sero groups 1 and 2 (S1 and S2). NIL 54 is recommended for further pathogenicity investigation with more isolates of RYMV in Nigeria or elsewhere, since, no obvious symptom of the virus was observed on the plant when challenged with S2 and S1 isolates in the present study.
J.T. Onwughalu, M.E. Abo, A.O. Nwankiti, J.K. Okoro and D. Silue, 2020. Determination of Pathogenicity Relationships of Rice Yellow Mottle Virus (RYMV) Isolates on Near Isogenic Lines (NILs) and Some Released Oryza Species in Nigeria. Research Journal of Applied Sciences, 15: 27-35.